Viron: transmissible state of a
virus. These structures contain a nucleic acid core wrapped in
a protein coat. This coat is called a capsid. Some virons
contain an envelope, constructed from the host cell membrane.
The nucleic acid core may be DNA ( double strand, single
strand), or RNA (single strand, double strand), but never both.
The shape of these virons vary from spherical, cylindrical,
bullet-shaped , to amorphous shaped particles. They vary in
diameter from 18 to 300 nm. Virons must infect a living cell.
Viruses are obligate intracellular parasites. Some virons are
hardier than others (hepatitis virus can withstand short
periods of boiling; most virons are destroyed by
this).

Viral Replication: most viruses
carry the enzyme RNA replicase to make complementary RNA
strands. Some viruses contain the enzyme reverse transcriptase,
which produces DNA , then RNA. These are called retro viruses.
HIV is an eample of a retro virus. The three basic patterns of
genome replication are: DNA--->DNA, RNA---->RNA, and
RNA------->DNA---->RNA. Viral components are held
together by weak bond ( van derWaals forces and hydrogen
bonds).

Host Specificity: Each type of virus can
infect and parasitize a limited range of host cells. They are
guided by external recognition areas of the host cell. This may
keep a virus from infecting many different types of
cells.

Lytic Cycle: Life cycle of virulent
phages.

1. The phage lands on the host cell, and
using 140 ATP's in its tail fibers, injects its nucleic acid
core into the bacterium.

2. The host's DNA is cut up and destroyed
by the enzymes produced by the host from the new
DNA.

3. The now unassembled nucleotides are
reassembles into phage DNA, which produces copies of the
capsid.

4. The genes also produce the enzyme
lysozyme, that digests the bacterial cell wall, causing the
newly assembled viruses to escape.

Lysogenic Cycle: Viruses that
reproduce without killing their hosts are called temperate
viruses. These viruses have 2 alternate forms of reproduction.
The lytic cycle or the lysogenic cycle. The process begins very
similar to the lytic infection or inserting the genome into the
host's genome and becoming dormant. During the lysogenic cycle
one of the temperate phage's genes remains active. It codes for
a repressor protein keeping the prophage genes inactive. From
here on the cells reproduce regularly. Each carrying the hidden
genes of the virus. Under normal circumstances harmless
bacteria remain so until infected by these viruses; then they
can become pathogenic. Example Botulism, diphtheria, and
scarlet fever bacteria.